We _________ the difficulty together, but why didn’t you tell me?
Once new difficulties _____ in our new job, we should learn to use our brains to solve them.
He has written a book_______I have forgotten.
This is the best chance for you to go abroad. Don't ________.
---Have you ________? ---No. I had the wrong number.
— Are you sure the delegation will come to our school next week? — _____. The head of it has just emailed me about the departure time of their flight.